As is known, a heavy goods vehicle tire tread comprises grooves of circumferential or longitudinal overall orientation (overall orientation is to be understood here to mean that these grooves extend in the circumferential direction, but that they may be straight or zigzagged). It is common place to differentiate the design of the tread pattern according to the axle on which the tire is mounted. When used on a driven axle, the tread of a heavy goods vehicle tire is also provided with a plurality of grooves of transverse overall orientation (what is to be understood here by a transverse overall orientation is that the mean direction of these grooves may be parallel to the direction of the axis of rotation of the tire or make an angle other than zero with the said axis).
The circumferentially and transversely orientated grooves of such a tread delimit, at least in the middle part of the tread, at least one row known as “intermediate row” formed of a succession of elements in relief in the form of blocks of rubber compound, these blocks having mean heights equal to the depth of the grooves that delimit them.
Each block comprises a contact face intended to come into contact with the road surface during running, and lateral faces that divide up the said contact face to form edge corners. The edge corner that is first to come into contact with the road surface during running corresponds to the edge corner known as the “leading edge corner” and is formed by the intersection of the contact face with a lateral face known as the “leading face” of the block, and the edge corner that is last to leave contact is known as the “trailing edge corner” formed by the intersection of the contact face and a lateral face known as the “trailing face”.
It is also known that under certain running conditions, the trailing edge corners of the blocks of the intermediate rows are subjected to more pronounced wear than the leading edge corners of the same blocks (leading to an uneven wear mechanism known as “saw-tooth” wear).
Solutions to this problem have been proposed in the past, and include the one described in patent U.S. Pat. No. 5,127,455. That document recommends inclining the leading face by a greater angle than the angle of inclination of the trailing face and limiting the angle between the leading face and the trailing face to at least 15 degrees and at most 25 degrees. In the aforegoing, the angle of a face is measured, in a plane of section perpendicular to the axis of rotation, with respect to a perpendicular to the running surface; the leading and trailing faces are inclined in such a way as to increase the width of the block with depth (and so the width of the groove between two blocks decreases as the tread wears away). The arrangement recommended in U.S. Pat. No. 5,127,455 gives this tread a single direction of running which is shown on the tread itself or on the tire provided with the tread using a visible means that indicates the said direction of running and thus ensures that the tire is mounted on the vehicle in the correct direction so that the full benefit of this differential inclination can be realized.
Furthermore, in order to achieve better grip on a wet road surface, each block may be provided with at least one incision (that is to say a cut the opposing faces of which are a mean distance of less than 1 mm apart. On each block provided with an incision, there are then created two additional edge corners that are useful for cutting into the film of water present on the road surface in rainy conditions.
However, it has been found that combining at least one incision with blocks as proposed in U.S. Pat. No. 5,127,455 could appreciably affect the wear rate of the blocks of the intermediate rows of a tread to the point that some of the supposed benefits could be lost by the creation of incisions in the blocks of these rows.